Central Heating Expansion Tank Problem

PC452

Hi there,
I'm new to this forum but I'm wondering if anyone can help. I have just had my central heating system flushed because the rads had cold patches and I was told that sludge had built up over the years and needed flushing. This is a very old system, must be 20/25 years and probably the most basic setup: oil fired boiler, no zoning (so no motorised 3 way valve to switch between CH and HW), no thermostats except that on the boiler. Despite it's age, the system worked OK apart from the radiator cold spots.
However, since the flushing (by what was supposed to be a professional plumber), the overflow has been leaking. He has been back to it 3 times now and replaced the ballcock, balanced the system and tried further tweaks. It was fine for a couple of hours and then the problem started again. So, I decided to go into the loft to have a look myself. The ballcock is fine (there is no water dripping from it). I part emptied the expansion tank (rusty, yellowy water) to a couple of inches below the overflow outlet, enough so that the ballcock didn't start letting water flow. However, within a couple of hours, the water level has risen and the starts overflowing again. This is without firing up the boiler, in other words, just leaving the system idle. I notice that when I turn the stopcock off at the mains, the water level does not rise. There are 3 pipes in the expansion tank (you guys know this anyway!) - the ballcock assy, the overflow and an outlet at the bottom which I am assuming is from the boiler/pipework. So, it would seem that water is coming in via this pipe. But how can this be with the system idle? Any help you guys can give would be so much appreciated. Thanks in advance.
PS: I've remembered something else about this: while the guy was flushing the system, he asked me if I wanted the pump replacing because the existing one was 13 years old. He put one on and after he left, I noticed hot water spewing from the overflow. The radiators were stone cold. I turned the boiler off and the pump was red hot. I got him back and he said that the pump must be faulty so I went to the local plumber's merchant and bought a brand new one myself which he fitted. Don't know if this helps anyone diagnose the problem. Thanks

Wearb

Is your Expansion tank lower that the main (bigger one) water tank?

PC452

It is in the loft on the same level as the header tank. Thank you.

Wearb

PC452 wrote: »

It is in the loft on the same level as the header tank. Thank you.

Could be a leak in your cylinder coil.

John.G

PC452 wrote: »

It is in the loft on the same level as the header tank. Thank you.

The next time it starts overflowing ensure that there is no demand for either cold or hot (domestic) water & no toilet flushing and if the cold water storage tank ballcock is still making up then you have a holed cylinder coil. The water level in the cold water storage tank would have to be level with, or above the F&E tank overflow for this to happen except that your hot water cylinder is pressurised with a pumped system.

_Brian

Wearb wrote: »

Could be a leak in your cylinder coil.

This is wit I would think.
Leak in the coil and the heating system is taking in water from the hot water system.

PC452

That's what I feared, thanks. I'm now thinking about having an oil combi boiler installed and doing away with the cylinder. I don't suppose you have any knowledge or experience of these have you? Many thanks

PC452

Thanks everyone for your replies and your expert opinions. Just another thought - is there a valve that the plumber who flushed the system would have to open to carry out this procedure and then forgot to close it?

Wearb

PC452 wrote: »

That's what I feared, thanks. I'm now thinking about having an oil combi boiler installed and doing away with the cylinder. I don't suppose you have any knowledge or experience of these have you? Many thanks

Lots of lads here like them, but I don't. Can be difficult to get a good tech to repair or service in areas where theyre uncommon. There can also be performance issues if not water usage is ignored when deciding on requirements.

Most of my concerns would be asuaged by a good installation and backup.

John.G

PC452 wrote: »

Thanks everyone for your replies and your expert opinions. Just another thought - is there a valve that the plumber who flushed the system would have to open to carry out this procedure and then forgot to close it?

I'd certainly check out if in fact you have a holed cylinder coil, did you check out the water level = overflow and is the cold water storage tank ballcock making up with no usage?

Wearb

PC452 wrote: »

Thanks everyone for your replies and your expert opinions. Just another thought - is there a valve that the plumber who flushed the system would have to open to carry out this procedure and then forgot to close it?

I can't think of any situation where that would cause the problem described.

PC452

Thanks everyone for your replies. The problem was a hole in the cylinder coil. New cylinder fitted and the problem has now been solved. Thank you, much appreciated.

Wearb

PC452 wrote: »

Thanks everyone for your replies. The problem was a hole in the cylinder coil. New cylinder fitted and the problem has now been solved. Thank you, much appreciated.

Thanks for getting back to us with final result. Its always goo to know what happened in the end.